The present invention relates to a method and an apparatus for thermal recording by means of a flying spot.
Thermal imaging or thermography is a recording process wherein images are generated by the use of imagewise modulated thermal energy. Most of the direct thermographic recording materials are of the chemical type. On heating to a certain conversion temperature, an irreversible chemical reaction takes place and a coloured image is produced. A particular interesting direct thermal imaging element uses an organic silver salt in combination with a reducing agent. Such combination may be imaged by a suitable heat source such as e.g. a thermal head, a laser etc.
A black and white image can be obtained with such a material because under the influence of heat the silver ions are developed to metallic silver. However, it appears to be difficult to obtain a neutral black tone image. Furthermore, it appears to be difficult to obtain a sufficiently high density as required in certain applications (e.g. in graphical applications).
Thermal recording information on a thermographic material by means of so-called xe2x80x9cflying spot scanningxe2x80x9d is well-known from the prior art.
The thermal recording can be carried out with the aid of different types of recording devices, e.g. a flat bed type recording (see FIG. 1), a capstan type recording device (see FIG. 2), an internal drum type ITD recording device (see FIG. 3) or an external drum type XTD recording device (see FIGS. 4, 5 and 6). An extensive description of such recording devices can be found e.g. in EP 0 734 148 and in U.S. Pat. No. 5,932,394 (both in the name of Agfa-Gevaert), so that in the present description any explicit and extensive replication is superfluous.
EP-A 0 485 148 discloses an image recording apparatus for recording an image by application of light beam to a photosensitive member, comprising: a photosensitive member; light source means for emitting first and second beams, one of the first and second beams bearing image information; and scanning means for scanning said photosensitive member with the first and second beams with a time interval so that they are overlapped on said photosensitive material.
EP-A 0 842 782 discloses a method of thermally recording a gradation image on a thermosensitive recording material (S) having a photothermal converting agent for converting light energy into thermal energy to develop a color at a density depending on the thermal energy, comprising the steps of: applying a laser beam (L) having a level of light energy depending on a gradation of an image to be recorded on the thermosensitive recording medium (S); and scanning the thermosensitive recording medium (S) with the laser beam (L) at a speed of at least 5 m/s.
EP-A 1 104 699 discloses a method for recording an image on a thermographic material (m) comprising the steps of: providing a thermographic material having a thermal imaging element (le), a transparent thermal head (TH) having energisable heating elements (Hi), and a radiation beam (L), activating heating elements of said thermal head and imagewise and scanwise exposing said imaging element by means of said radiation beam, such that the total energy resulting from said thermal head and from said radiation beam has a level corresponding to a gradation of the image to be recorded on said imaging element, wherein said imagewise and scanwise exposing is carried out by passing said radiation beam through transparent parts of said thermal head.
U.S. Pat. No. 5,932,394 discloses a method for generating on a lithographic printing plate a screened reproduction of a contone image, comprising the steps of: (1) transporting a thermosensitive imaging element through an exposure area, the imaging element having thereon at least one scan line including a plurality of microdots, at least one microdot being an effective microdot; (2) scanwise exposing said thermosensitive imaging element according to screened data representative for tones of a contone image with a set of radiation beams as said thermosensitive imaging element is transported through said exposure area, at least one of said radiation beams being an effective radiation beam, at any given moment during said exposure at least two radiation beams of said set of radiation beam impinge on different microdots of a scanline on said imaging element, so that by completion of the exposure step each effective microdot of said scanline has been impinged by all effective beams of said set, wherein said thermosensitive imaging element includes an image forming layer on a hydrophilic surface of a lithographic base, said image forming layer comprising hydrophobic thermoplastic polymer particles and a compound capable of converting light into heat, said compound being present in one of said image forming layer and a layer adjacent thereto.
Thermal recording according to the prior art by means of a flying spot laser on a thermographic material generally only gives a sufficient density if the energy radiated by the laser beam is so high that unwanted side-effects occur (e.g. burning, shrinkage and irregular expansion). If one diminishes the energy in order to eliminate such side effects, the output density is unacceptably low.
This problem in particular applies to graphical applications often requiring optical densities greater than 3.0 or 4.0 or even 5.0 D. In addition, high spatial resolutions as e.g. higher than 600 or even 1200 dpi are often required or small line-widths e.g. smaller than 40 or even 20 xcexcm or fine pixel-sizes e.g. finer than 40 or even 20 xcexcm.
It is an aspect of the present invention to provide an apparatus for thermal recording which is capable of yielding images with improved tone neutrality.
It is a further aspect of the present information to provide a method for recording information, which is capable of yielding images with improved tone neutrality.
Further aspects and advantages of the invention will become apparent from the description hereinafter.
Aspects of the present invention are realized by an apparatus for thermal recording an image in a substantially light-insensitive thermographic material m having a burning temperature Tb, the substantially light-insensitive thermographic material m comprising a thermosensitive element having a conversion temperature Tc a support, and at least one light-to-heat conversion agent, comprises a means for generating a radiation beam 20 including wavelengths xcex absorbed by the light-to-heat conversion agent and an optical means of scanning a line 40 of the substantially light-insensitive thermographic material m with the radiation beam 20 at different positions thereon along a scanning direction at each point of time in a scanning cycle.
Aspects of the present invention are also realized by a method for recording information, comprising the steps of: providing an apparatus for thermal recording 1, the above-mentioned substantially light-insensitive thermographic material m (5); generating a radiation beam 20 including wavelengths xcex absorbed by the light-to-heat conversion agent and being modulated in accordance with the information to be recorded; scanning a line 40 of the substantially light-insensitive thermographic material m a first time with the radiation beam, thereby heating the line of the substantially light-insensitive thermographic material m to a first predetermined temperature T1 being above the conversion temperature Tc and below the burning temperature Tb of the substantially light-insensitive thermographic material m; re-scanning the same line of the substantially light-insensitive thermographic material m a plurality of times ns with the same radiation beam being identically modulated in accordance with the information to be recorded.
Aspects of the present invention are also realized by the use of the above-mentioned method in laser thermography.
Further advantages and embodiments of the present invention will become apparent from the following description and drawings.